net: sfp-bus: constify link_modes to sfp_select_interface()

sfp_select_interface() does not modify its link_modes argument, so
make this a const pointer.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://lore.kernel.org/r/E1s15s0-00AHyq-8E@rmk-PC.armlinux.org.uk


Signed-off-by: Paolo Abeni <pabeni@redhat.com>